The present invention is generally drawn to lighter-than-air (xe2x80x9cLTAxe2x80x9d) devices and respective uses thereof.
Although there are many examples of connections between the ground and LTA devices, the barrage balloon is the only reported example of an LTA device designed primarily to control the space beneath itself. The barrage balloon was designed to damage or destroy an airplane that flew into the cable between the balloon and the ground. Today Federal Aviation Agency regulations require posting a NOTAM (Notice to Airmen) in addition to marking the aerostat or tethered balloon""s tether cable whenever flown, to prevent its unintentionally serving as a barrage balloon.
An LTA device remains airborne because it consists primarily of a buoyant gas, such as hot air or some other gas which weighs less than the air that it displaces. For example: Under Standard Sea-level temperature and pressure conditions, one thousand cubic feet of helium displaces one thousand cubic feet of air, thus providing roughly 64 pounds of lifting force.
Non-limiting examples of buoyant gases to be used in LTA devices include hydrogen, helium, methane, and pipeline gas (natural gas). Hydrogen provides the most lift, but is highly flammable. Helium, which is not flammable, provides nearly as much lift as hydrogen, but is much more expensive than hydrogen. Methane is nearly half as effective a lifting gas as helium, but also is flammable. Natural Gas, because of heavy impurities, is slightly less effective than pure methane, but is widely available and very inexpensive compared to hydrogen, helium or methane.
Accordingly, a 10-foot diameter sphere provides a gross lift of approximately 270 pounds if filled with helium. Although a sphere is the most efficient container, enclosing the greatest volume with the least surface area, conventional balloon construction techniques require many panels and consequently many heavy seams. Thus, the fabric in a spherical balloon may weigh as much as a simple cylindrical balloon of equal volume, but with fewer seams.
Nineteenth century aeronauts invested a great deal of effort developing techniques using one or more appendages to provide the pilot some control over his balloon with respect to the prevailing wind and to take advantage of ocean or river currents. They repeatedly demonstrated that sails could be effectively employed to provide directional control if the balloon moved significantly slower than the relative wind. (Example: AIRSHIPS PAST AND PRESENT, Hildebrandt, A., Van Nostrand Co, New York, 1908. The first attempt to reach the North Pole by balloon (Andre""s Red Balloon) combined the use of a balloon mounted sail, and a weighted line which dragged in the water or over the ice.)
With the introduction of the internal combustion engine, aeronauts were finally able to move independent of the wind. However, their airship""s speed was limited both by propulsive power and by the effect of dynamic air pressure on the envelope and the airship appendages Conventional airships are still limited to roughly 80 miles per hour, with normal xe2x80x9ccruisingxe2x80x9d speeds in the 30 to 40 mph range.
Other problems associated with conventional airships deal with changes in air temperature, pressure, and the effects of condensation and precipitation. Specifically, while traveling through fog, or more generally clouds, condensation accumulates on the surface of the envelope. Such accumulation over the large surface area of the airship adds undesirable weight to the envelope, thereby adversely affecting the airship""s efficiency. In extreme cases, large amounts of water accumulation may be detrimental to the flight of the airship. Most airship designs incorporate features to prevent the dripping water from interfering with pilot visibility and to prevent ice thrown from the propeller blades from damaging the envelope. It was common military practice to fly into a summer shower near the end of a mission, primarily to cool the gas in order to bring the airship back to neutral buoyancy, and secondarily to wash the envelope. Since most flights were over-water, pilots found it more effective to use a winch to pick up ballast water when needed, rather than to hunt for rain,
During the first century of manned flight, balloons were normally inflated shortly before launching, and the envelope collapsed by releasing the gas at the end of the flight, in the same manner as the present-day hot-air balloons and airships. Because of the cost and complexity of rigging cold-gas airships, Santos-Dumont developed the hangar and other techniques for maintaining an inflated airship between flights.
Various techniques were developed, using one or more lines for ground handling, recovery, controlling and anchoring balloons and airships. During World War I, British, Italian, and other airship operators developed multi-point high-moors; the airship was commonly tethered thirty feet in the air. Alternatively, airships were xe2x80x9cbedded downxe2x80x9d; tethered closely to the ground and protected by natural or manmade windbreaks or shelters if they could not be safely returned to a hangar. The Russian""s reported that one of their bedded down airships (SSSR V2, on bivouac) tore loose from sixty xe2x80x9ccorkscrewxe2x80x9d ground anchors and was blown away on Sep. 6, 1935.
Since the development of the mooring mast shortly after World War I, nearly all American airships have been designed to operate from a fixed or mobile mooring mast. Typically, the airship is ballasted to near-neutral buoyancy, connected to the mast by a fitting at its nose, and allowed to weathercock around the mast. High winds or unexpected wind shifts and gusting, while the airship is attached to a mooring mast, or while groundhandling crews are moving the airship, continue to be primary causes of airship losses and accidents.
An airship""s lines, ropes and/or cables may be manhandled, fastened to powered winches on land or specially modified ships or heavy vehicles or attached to fixed and drifting anchors. Airship and aerostat lines have been used to carry electrical power, water, gas, telegraph, telephone, analog and digital electronic signals and electro-optical signals between the ground and the buoyant device. Airship""s winches have been used to tow boats and sonar-bodies, to transfer passengers, and to pick up other loads from the ground and the sea. However, as previously mentioned, except for the barrage balloon, no applications were designed to control or use the space between the balloon and the earth, except to protect and secure the LTA device itself.
What has not been developed is a system and method to control the space between the earth and the LTA device. What is further needed is a means of controlling the height, orientation and disposition of the system as well as rapid retrieval and stowage at the onset of severe weather or whenever the operator needs to deactivate the system for some other reason.
Rather than using a mooring mast, or multiple lines to constrain and control the LTA device, this invention employs a flexible distributed surface, a surface which in addition to restraining and controlling the LTA device also performs, inter alia, one or more of the following useful functions: blocks light; screens, filters, and/or blocks airflow; collects and condenses aerosols; blocks or stops larger airborne particles, bugs and birds.
It is an object of this invention to provide a working surface to limit and control the movement of air between an LTA element and the earth beneath it.
It is another object of this invention to provide a working surface to limit and control the movement of objects or materials in the air between an LTA element and the earth beneath it.
It is still another object of this invention to provide a method and system to limit or control light and other radiation effects through this working surface.
It is still yet another object of this invention to provide a method and system for rapid erection and relocation of an extremely lightweight, large wall or curtain over/around virtually unprepared terrain or water surfaces.
The present invention uses an LTA device, non-limiting examples of which include balloons, aerostats or airships, to support the upper end of one or more extended working surfaces between the device and the ground or the sea. In most applications the device will be operating at very low altitudes (the working surface less than 500 feet in height) and operating in light winds (less than 15 knots). Consequently the LTA device""s design and strength requirements are considerably relaxed vis-à-vis conventional airships and aerostats.
The working surface may be built as a part of the balloon structure, or may be designed for rapid attachment/detachment and replacement. Suitable materials for the surface range from impermeable fabrics to open web nets, depending upon the intended application. The working surface may be opaque, transparent, or translucent. The surface may be created as a unitary fabric or assembled by connecting multiple segments of similar or dissimilar fabrics. An individual working surface may incorporate embedded or attachable power and signal lines, special tensile strength members and attachment points, such as eyelets or xe2x80x9cVelcroxe2x80x9d pads.
In some applications more than one such surface may be supported by the same LTA element and connected to separate ground attachments. In other applications, surfaces may be arranged as a cascade, between two or more buoyant balloons or airships.
Applications include, inter alia: fog clearing/harvesting; air dam/wind break; turning vane for windmills; stirring vane for frost prevention; sail, primary or secondary ship propulsion; and various mechanical and visual barrier (filter, screen, fence and reflector) applications.
As a fog harvester, the present invention works best under calm or light wind conditions. The large exposed surface and its supporting balloon, with or without additional cooling, efficiently condenses and collects airborne aerosols. If there is insufficient wind, or if the purpose is to clear fog from a specific area, such as an airport runway, the entire assembly can be propelled against the wind down the entire length of the runway.
In another application, the invention can be attached as a segmented skirt, connecting a low-tethered balloon, such as the Lindstrand HiFlyer, which uses an eighteen cable tie-down system. The HiFlyer would then resemble a large inverted cone, but serve as an extremely large tent.
In its simplest application, the invention consists of a single flexible film, attached at intervals to the bottom of a cylindrical LTA balloon by its strength members (cables, cords or reinforcing tape or webbing), and also attached at its bottom to hard points on the ground, thus forming a surface in tension as a result of the lifting force of the balloon. Guys, at one or both ends of the balloon may be used to orient the balloon and thus the surface to the wind, or the balloon might be left free to respond to the wind""s force and be tethered only through the working surface.
The balloon may be parallel to the ground or it may be adjusted to an arbitrary angle, as in a lateen sail. The ground attachments may be in a straight line, in an arc, or any other desired configuration to control the orientation of the surface and/or to adjust the area of the working surface exposed to the sun and/or wind.
For illustrative purposes, consider a two hundred foot long cylindrical balloon, twenty feet in diameter. Such a balloon filled with approximately 62,000 cubic feet of helium, would provide a gross lift of roughly 20 pounds per foot of length (about 10 pounds per foot if filled with methane). Under calm conditions, the working surface, a xe2x80x9ccurtainxe2x80x9d rising from ground level to the balloon would present a nearly vertical surface. Under light wind conditions, or when the base is moved relative to the earth, the force of the apparent wind against the curtain will drive the balloon to windward, until the buoyancy, gravity, inertia, and wind forces reach an equilibrium.
In general, the present invention provides an LTA device comprising, a buoyant element containing LTA gas, and a flexible surface having a length and height forming a usable area, the length of the flexible surface being connected directly to the buoyant element, wherein the flexible surface is operable to use an area defined by the buoyant element and line below the flexible surface.
In general, the present invention further provides a method of condensing water comprising, inflating an element with sufficient LTA gas to lift the element and at least a portion of a flexible surface, the flexible surface having a length and height forming a usable area connected directly to the buoyant element, off the ground, and controllably moving the inflated buoyant element and the flexible surface through the air, wherein water condenses on the buoyant element and drips down the flexible surface.
The present invention still further provides a method of powering a vessel, in favorable winds, by using the working surface as a sail secured to the vessel, the sail having length and height and being connected directly to the buoyant element, and inflating the element with sufficient LTA gas to lift the element and at least a portion of the sail off the vessel, wherein wind force pushes the sail and therefore moves the vessel.
The present invention yet further provides a method of blocking material from entering an area, securing a flexible surface to a perimeter of the area, the flexible surface having a length and a height and being connected directly to an element, and inflating the element with sufficient LTA gas to lift the element and at least a portion of the flexible surface off the ground, wherein flexible surface lifted by the inflated element prevents material from entering the area. In one embodiment, the material blocked from entering the area is turbulent air. In another embodiment, the material blocked from entering the area is fog. In yet another embodiment, the material blocked from entering the area includes liquid or solid objects, such as insects.
Additional advantages of the present invention will become apparent to those skilled in the art from the following detailed description of exemplary embodiments of the present invention. The invention itself, together with further objects and advantages, can be better understood by reference to the following detailed description and the accompanying drawings.